Tuesday, November 11, 2014

The Science of Interstellar Q&A

Firstly, a huge credit to Christopher Nolan for producing such a wonderful film.
I like the character of Mr Cooper and Professor Brand. Anne Hathaway's character—apart from her stunning look—doesn't really appeal to me; some of her lines are clearly misplaced, like the one when she starts murmuring about how love transcends gravity and shit-I-can't-even-recall-because-it's-so-cheesy-and-embarrassingly-bad-I-mean-wtf-you're-being-illogical-as-a-scientist.

One pleasant surprise though: Nolan enlisted Caltech physicist Kip Thorne as the film's technical adviser, which explains why most non-physicists find the film so difficult to understand.

1) What is the Dust Bowl?

The dust bowl scene in the movie did actually happen in the past. During the 1930s, a series of prolonged drought severely ravaged the ecology and agriculture of the US and Canadian prairies. The dry spell led to desertification and subsequently, severe dust storms.
During the dust bowl, the dry soil turned to dust, which the prevailing winds blew away in huge clouds that sometimes blackened the sky. People had to put their glasses and plates upside down to prevent dusts from settling on them.

So the scene shown in the movie is a real phenomenon.

2) Why does the Endurance spin?

We all have seen clips of astronauts floating in space on Youtube and documentaries, thanks to the lack of gravity in space.

But there's a way to create a sense of weight in space; and that's by spinning the
spaceship. When the spaceship spins, the astronauts are being thrown out (refer figure below), while the floor of the spaceship "pushes up" against the feet of the astronauts, making them feel like they're actually stepping on something, and thus a sense of weight.

Having a sense of weight in space allows the astronauts to better adapt to the condition of outer space and to better do their chores. The spinning motion must be accelerating i.e. getting faster and faster to maintain the sense of weight, a difficult but not impossible task.

3) What's a Wormhole?

The theory of general relativity suggests the existence of "bridges" through space-time. These paths, called Einstein-Rosen bridges or wormholes, connect two different points in space-time, theoretically creating a shortcut that could reduce travel time and distance.—space.com

Wormhole. Image: edobric/Shutterstock

Referring to the above image, consider going from point A to point B. So instead of taking the conventional path (red line), a wormhole creates a short cut from point A to B (green line), enabling us to travel to point B using much shorter time and path, or to places otherwise deemed too far or downright impossible to reach.

4) What's a Black hole?

When a star with huge mass dies, it turns into either a black hole or a neutron star. Those that become black holes literally suck, because as Einstein explained: the more massive something is, the more gravity it produces. So black holes have gravity so powerful they actually suck in light (I mean, how is that even possible?!) and pull space and time with it.

The computer effects team of the film based their visualization on Thorne’s equations. When they did, the accretion disk appeared all around it: “above the black hole, below the black hole, and in front of it.” Thorne wasn’t expecting this, but says that he now sees that this is what his equations dictate.

6) Can planets orbit around black holes host life?

Highly unlikely.
Firstly, black holes are dead stars. When a star dies, it explodes in a massive explosion called the supernova. After the explosion the dead star loses all its energy. Without energy, where do you get the light from? No light, no photosynthesis.

Moreover, the gravitational pull of a black hole is so strong not even
light can escape its pull. In order to
safely orbit the black hole, an object should be at a distance
equivalent to at least three times the gravitational radius of the black hole itself, otherwise it would fall into the event horizon
and disappear into the black hole. In the movie, however, the three
planets are so close to the black hole it's a wonder they don't get
sucked in.

In the movie, there is a beam of light enveloping the Gargantua black hole. It's called the accretion disc, a flat swirling disk of material that is being slowly sucked into the black hole. Some may argue that the light coming off the disc could light up and warm the three planets. But if the planets were really at a distance equals to three times the gravitational radius of the black hole, the light and warmth coming off the accretion disc alone might not be enough to light up the planets at all.

7) Why is a day on the first planet equals to seven years on the spaceship?

This is called time dilation. It's a phenomenon made possible (and famous) by Einstein's theory of relativity.
You can get affected in several ways; firstly, if you move at a speed close to the speed of light, your time passes slower; secondly, if you're near or in a place where the gravity is very strong, your time passes slower.
In the movie, Mr Cooper and Dr Brand go to the first planet, which has a 1.3 time the gravity of Earth. Factor in the black hole nearby and we get a 7-year-per-hour time dilation. That's a ludicrously high number. But I can't check the math because I don't have all the values and parameters so I'll just let it be.

8) Can a human survive a black hole?

No. Cooper survives the plunge for reasons unknown, and for that I was pretty upset.

The gravitational pull from a black hole is so intense that the feet of the astronaut would feel a different force than his head, because his head is a tad further than his feet to the black hole. And as a result his feet will be pulled by a force so huge his body will be stretched, like a spaghetti, and torn apart before he even reaches the black hole.

Not exactly. Stephen Hawking discovered that something does leak out from black holes; it's called the Hawking radiation— a black body radiation emitted from black holes due to quantum effects. Hawking radiation causes black holes to lose its mass and the energy gradually, therefore slowly shrink and ultimately vanish.

Last I checked, humans are neither black body nor radiation. So I'm pretty sure that no humans could possibly go inside a black hole and come out unscathed.

11) The tsunami on the first planet killed Mr Doyle. In reality is it really possible to get a tsunami that huge?

Yes. There are seas of diamond on Neptune and Uranus—literally seas filled with liquid diamond. And there's the Great Red Spot on Jupiter— a long-lived enormous storm system on the planet Jupiter approximately 16,500 km wide—large enough to engulf Earth. Foreign planets are weird. So a massive tsunami on a foreign planet can be a common thing.

12) During one of the scenes Mr Cooper spins the Ranger spaceship to align itself with the exploding Endurance, and Dr Brand passes out. What happened?

When you make a sharp turn in your car, you can feel yourself being pulled to the opposite side. Similarly, when you move faster, for example piloting a fighter jet, and make a sharp turn upward, you'll feel a strong force pulling you downward.
This is called the G-force. 1 G is the amount of gravitational pull exerted on your body. 2 G means you feel twice the weight of your own body. So if you're 50kg, and you feel 3 G, it means you feel as if you weigh as much as 150 kg. A NASA document showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.

But the spacecraft in Interstellar spins at 68 rpm, and assuming that the distance of the pilot to the spinning axis is a modest 20 meter, the amount of G-force exerted on the pilots would be an astounding 103.4 G. No human—not even one with a highly specialized pressure suit—in my opinion, could have survived that. What's even more incredible is that Mr Cooper managed to pilot the spaceship for more than 10 seconds to allow the ship to dock the Endurance.
13) During the final part of the film, Mr Cooper says they have not enough fuel to make it to Edmund's planet, so they will employ the gravitational slingshot method. WTF is that?

It's actually a way to save rocket fuel.
The problem with rocket, you see, is that they need to travel far with the little fuel they carry. So in order to maximize the distance they can travel, scientists and engineers program the rockets to follow a certain path, sneak up to a planet and steal its angular momentum.

Consider a rocket X travelling to Uranus from Earth. It will first be launched from Earth and stays in the Earth's orbit. When Mars approaches, the rocket starts its engine and propels itself to reach the gravitational pull of Mars from its back.
As the spacecraft come into Mars' gravitational influence, it fell toward the planet, increasing its speed toward maximum at closest approach to Mars. The gravity of Mars speeds up the spacecraft substantially to a speed greater than its escape velocity, thus enabling rocket X to travel to further destination without crashing onto Mars. It leaves the area near Mars faster and in a different trajectory. This technique was repeated at Jupiter and Saturn.

Conclusion
Despite the movie's scientific shortcomings, I can't complain much about this movie really. I've made several short clips myself and I know that sometimes, in order to keep the plot going/interesting, you need to make up fictional stuff and sacrifice the facts. Science can be fascinating, but try imagine the reaction of the audience, if they were told the time dilation was 2 minutes instead of 23 years—a mere 2-minute time dilation could hardly leave a similar impact on the audience as a 23-year delay.
So in this case, science gives way to storytelling.